1. Field of the Invention
The present invention relates to a magnetic head for reading data from and/or writing data on a magnetic disk as a magnetic recording medium.
2. Description of the Prior Art
There are various types of conventional magnetic heads, for reading data from and/or writing data on a floppy disk (a flexible magnetic disk) by so-called tunnel erasing technique. One of them is illustrated in FIGS. 7 through 9 as an example.
FIG. 7 is an exploded perspective view showing a magnetic head main body, which is a component of the magnetic head shown in FIG. 8. As shown in FIG. 7, reference numeral 1 denotes a front core assembly (to be called the "core assembly" for short) which has a unitary construction consisting of a magnetic read/write core (to be called the "read/write core" for short) 2 and a magnetic erasing core (to be called the "erasing core" for short) 4 for executing the tunnel erasing technique. These cores 2 and 4 are integrally joined together by a spacer 6, which is placed between two I-shaped front core portions 2b and 4b.
The read/write core 2 is fabricated by integrally joining the upper end of the I-shaped front core portion 2b to an upper end of a T-shaped front core portion 2a through a read/write gap 3 and by integrally joining a back core portion 15 to the lower ends of the two front core portions 2a and 2b. The erasing core 4 is fabricated by integrally joining the upper end of the I-shaped front core portion 4b to a T-shaped front core portion 4a through erasing gaps 5 and 5' and by integrally joining a back core portion 16 to the lower ends of the two front core portion 4a and 4b. Before the back core portion 15 and 16 are joined, the read/write core 2 and the erasing core 4 are joined together with the spacer 6 inserted between them, and then nonmagnetic sliders 7 and 8 are joined to the outer surfaces of the two cores 2 and 4 with adhesives or glass bonding and the like. As will be described in detail hereinafter, after coil bobbins 9 and 12 are mounted on the front core portions 2a and 4b, respectively, the back core portions 15 and 16 are joined to the lower ends of the core portions 2a and 4b. The sliders 7 and 8 slide on a magnetic disk (not shown) in order to ensure that the cores 2 and 4 are in stable sliding contact with the magnetic disk and in order to protect them. The sliders are made of ceramic or the like and are L-shaped in cross section. The sliders have cutout portions 7b and 8b, sliding contact surfaces 7c and 8c for making sliding contact with the magnetic disk, and bond areas 7a and 8a for joining with the cores 2 and 4, respectively. The core assembly 1 is sandwiched between the bond areas 7a and 8a of the sliders 7 and 8, which are joined to the core assembly 1 in the direction of its thickness.
The coil bobbin 9 has a read/write coil 10, and the coil bobbin 12 has an erasing coil 13. Both of the bobbins 9 and 12 are fitted on the front core portions 2a and 4a of the core assembly 1, respectively. Thereafter, the back core portions 15 and 16, which are integrally joined together through a spacer 17, are joined to the lower ends of the front core portions 2a, 2b, 4a and 4b.
FIG. 8 illustrates a magnetic head 21 fabricated by securely mounting a magnetic head main body 18 constructed by assembling the above-described components on a supporting plate 19 made of stainless steel or beryllium, copper, and by electrically connecting the ends of the coils 10 and 13 to a flexible printed circuit board 20 connected to the supporting plate 19.
The magnetic head 21 is mounted in a disk drive device (not shown) by securely joining the supporting plate 19 on a head carriage (not shown). The core assembly 1 and the sliding surfaces 7c and 8c of the sliders 7 and 8 slide on the magnetic disk so as to write information thereon by the tunnel erasing technique shown in FIG. 9. More specifically, in the tunnel erasing technique, after data is recorded on the magnetic disk by way of the read/write gap 3 in contact with a magnetic disk moving in the direction indicated by an arrow in FIG. 9, both sides of the recorded data are erased by a pair of the erasing gaps 5 and 5' so that a data track 22 with a predetermined width is defined on the magnetic disk.
Now, the capacity of floppy disk storage has been increased in recent years and the floppy disks which are able to record 10 megabytes or more are now available in the commercial market. The high capacity can be attained by increasing not only the line recording density but also the track density. In the case of a conventional floppy disk with a capacity on the order of 1 or 2M Bytes, the maximum line recording density is 9.7K Bytes and the track density is 135 TPI (Tracks per Inch), but in order to attain a capacity of 10M Bytes or over, both of the line recording density and the track density must be increased about three to four times; that is, the maximum line recording density must be in excess of 35K BPI (Bits Per Inch) and the track density must be in excess of 405 TPI.
In order to increase the track density, instead of a tunnel erasing type magnetic head such as the magnetic head 21 shown in FIGS. 7 and 8, a servo signal type magnetic head can be used when the so-called embedded or buried servo technique is employed. Servo information is written to the magnetic disk when it is manufactured.
Referring now to FIG. 10, the method for writing data on the magnetic disk by the servo signal technique will be described. According to this technique, the position of a track is determined in response to servo signals 24 previously recorded on the magnetic disk, and the data is recorded by a magnetic head having only a read/write core 2 which has only a read/write gap 3, whereby the data track 22 is defined. Such a servo-signal type magnetic head can be used to attain a track density in excess of 200 TPI.
In case of a typical floppy disk, interchangeability between the high grade type of disk and the low grade type storage is demanded in order to ensure the interchanging of software and data. For instance, in the case of a 3.5 inch floppy disk with a data-packing density of 2 MB (Mega Bytes), it is now possible to effect a 1 MB R/W (read/write) interchange (that is, it is possible to write and read the 1 MB data) and in the case of a disk with a 4 MB data-packing density, R/W interchangeability between 1 MB and 2 MB is possible. In such disks R/W interchangeability is possible because the track density of the disks is the same 135 TPI. However, if the track density is different, it may be possible to read out the data from a floppy disk with a low track density, but data recording is impossible so that the conventional interchange of software and data is not satisfactory.
In view of the above, in order to ensure interchangeability even if the track density is different, one might consider a composite type magnetic head in which a tunnel erasing type magnetic core and a servo-signal type magnetic core are arrayed in parallel in the width direction of a track. FIG. 11 illustrates an exploded perspective view showing such a composite type magnetic head. The same reference numerals are used in FIGS. 7, 8, and 11 to indicate similar parts.
Referring now to FIG. 11, the tunnel erasing type read/write core 2 and the erasing core 4 which constitute the core assembly 1 are designed and constructed for a floppy disks with a track density of, i.g., 135 TPI. The core assembly 1 shown in FIG. 11 is different in construction from the core assembly shown in FIGS. 7 and 8, because the coil bobbin 12 of the erasing core 4 is fitted on the back core portion 16 in order to avoid interference with a coil bobbin 27 of a read/write core 40. Therefore, the length of the back core portion 16 is relatively increased and the front core portion 4a is similar in shape to the letter L.
The read/write core 40 is a servo-signal type magnetic core for reading data from and writing data on the magnetic disk. The core 40 is designed and constructed for use with a high track density (for instance, 405 or 540 TPI, or the like). The read/write core 40 comprises a front core assembly 25 (to be called the "core assembly" for short) and a back core portion 29. More specifically, the read/write core 40 is fabricated by joining an L-shaped front core portion 25a and a T-shaped front core portion 25b at their upper regions, leaving a read/write gap 26 between them, and further by securely attaching the back core portion 29 to the lower ends of the core portions 25a and 25b. The bobbin 27 holds a coil 28, and is fitted on the front core portion 25a before the back core portion 29 is joined on the core portions 25a and 25b.
Reference numeral 30 denotes a partition wall plate made of nonmagnetic ferrite or ceramic, and is interposed and securely joined by adhesion between the core assemblies 1 and 25. This partition wall plate 30 is an elongated rectangular plate corresponding in size to the upper ends of the front core portions 2a, 4a, 25a and 25b of the core assemblies 1 and 25. The sliders 7 and 8 are joined to the outer surfaces in the width direction of the tracks, respectively, of the core assemblies 1 and 25.
FIG. 12 illustrates a composite type magnetic head main body 31 fabricated by assembling the above-mentioned components. With this magnetic head main body 31, the core 2, 4 or 40 is suitably selected depending upon the difference in the track density so that read/write interchange between high and low grade apparatuses becomes possible.
However, in the case of the conventional composite head main body 31 described above, both the exposed surfaces of a pair of core assemblies 1 and 25 and the sliding surfaces 7c and 8c of the sliders 7 and 8 keep sliding contact with the recording medium (magnetic disk), and the sliding contact surface area is considerably larger than the sliding contact surface area of an apparatus of the type using only one magnetic core in a core assembly. As a result, when the magnetic head main body 31 is pressed against the surface of the recording medium, the contact pressure is distributed over additional parts beyond the read/write gaps 3 and 26 and the erasing gaps 5 and 5' of the magnetic head main body.
Consequently the contact force between the gaps 3, 26, 5 and 5' and the recording medium decreases, with the result of variation in the spacing between the gaps 3, 26, 5 and 5' and the recording medium, so that the read/write and erasing characteristics of the magnetic head 31 are worsened owing to the spacing increase.
In contrast with this, if the contact pressure mentioned above is increased in order to reduce the spacing, the recording medium is damaged and rubs onto the magnetic head main body 31, so that the reading, writing and erasing operations would be impossible.